Low-temperature low-stress blanket tungsten film

Abstract

A chemical vapor deposition process performed at a temperature below 440 degrees C. for blanket tungsten deposition as a step in manufacturing integrated circuits deposits an integrated film suitable for voidless fill of vias as small as 0.5 microns in width and with aspect ratios of more than 2, while providing resistivity well below 100 micro-ohms per square, film stress generally in the mid 7E+09 dynes per square centimeter and below, and reflectivity of more than 40%, measured relative to silicon at 436 nanometer wavelength for 1 micron film thickness, while avoiding the use of nitrogen in the process.

What is claimed is: 
     
       1. A method for depositing a blanket integrated film of tungsten by CVD from WF 6  reduced by H 2  on a surface to be coated of a semiconductor wafer, comprising the steps of: forming a first portion of the integrated film under conditions conducive to voidless via fill to fill any vias on the surface to be coated, the first portion deposited at a wafer temperature not exceeding 440° C., a total pressure of from about 20 Torr to 100 Torr, and a WF 6  flow of at least 0.15 sccm per square centimeter of wafer surface to be coated, the coating gases injected over the wafer surface through a gas distribution device at a distance no greater than about 5.0 cm;   forming a second portion of the integrated film under conditions conducive to a low film stress, the second portion deposited at a wafer temperature not exceeding 440° C., a total pressure of from about 20 Torr to 100 Torr, and a WF 6  flow no more than 0.05 sccm per square centimeter of wafer surface, the coating gases injected over the wafer surface through the gas distribution device at a distance no greater than about 5.0 cm.   
     
     
       2. The method of claim 1 wherein said first portion is deposited without the use of said gas distribution device. 
     
     
       3. The method of claim 1 wherein each of said first and second film portions are deposited in the absence of nitrogen. 
     
     
       4. The method of claim 1 wherein the integrated film attains a thickness of at least 0.8 micron, of which at least half of the thickness is deposited as said first portion. 
     
     
       5. The method of claim 4 wherein 60% or more of the final film thickness is deposited as said first portion. 
     
     
       6. The method of claim 1 wherein said first portion is deposited at a temperature of about 400° C., a total pressure of about 30 Torr, and with a WF 6  flow of about 0.22 sccm per square centimeter of wafer surface, and said second portion is deposited at a temperature of about 400° C., a total pressure of about 30 Torr, and with a WF 6  flow of about 0.04 sccm per wafer. 
     
     
       7. The method of claim 1 further comprising an additional and prior nucleation step before depositing said first and said second film portions, said nucleation step comprising deposition of tungsten to a thickness of from about 500 to about 1000 Å at a temperature not exceeding 440° C. at a total pressure not exceeding 0.5 Torr, comprising a flow of WF 6  of at least 0.20 sccm per square centimeter of wafer surface, and a flow of SiH 4  at least one-fifth of the WF 6  flow. 
     
     
       8. A method for depositing a blanket integrated film of tungsten by CVD on a surface to be coated of a semiconductor wafer in the absence of nitrogen, comprising the steps of: placing said wafer to be coated on a support in a CVD chamber;   heating said wafer to a temperature not exceeding 440° C.;   depositing a first portion of said integrated film to a thickness of at least 50% of the total integrated film thickness by: flowing WF 6  onto the surface to be coated at a flow rate of at least 0.15 sccm per square centimeter of wafer surface;   flowing hydrogen onto the surface to be coated in conjunction with flowing WF 6 , and at a rate of at least ten times the WF 6  flow rate; and   maintaining total pressure in the chamber of at least 25 Torr; and depositing a second portion of said integrated film by:   flowing WF 6  onto the wafer at a flow rate of no more than about 0.05 sccm per square centimeter of wafer surface;   flowing hydrogen onto the wafer in conjunction with flowing WF 6 , and at a rate of at least one hundred times the WF 6  flow rate; and   maintaining total pressure in the chamber of at least 25 Torr;     the coating gases injected onto the wafer surface through a gas distribution device at a distance no greater than about 3.8 cm.   
     
     
       9. The method of claim 8 wherein the temperature of the wafer to be coated is maintained at about 400° C. for deposition of both portions of the integrated film, the pressure is maintained at about 30 Torr for deposition of both portions of said integrated film, the flow of WF 6  is maintained at about 0.20 sccm per square centimeter of wafer surface for the deposition of said first portion of said integrated film, and the flow of WF 6  is maintained at about 0.04 sccm per square centimeter of wafer surface for deposition of the second portion of said integrated film. 
     
     
       10. A method for depositing a blanket integrated film of tungsten by CVD on a surface to be coated of a semiconductor wafer in the absence of nitrogen, comprising the steps of: placing said wafer to be coated on a support in a CVD chamber;   heating said wafer to a temperature not exceeding 410° C.;   depositing a nucleation layer at a total pressure not exceeding 0.5 Torr comprising steps of: flowing WF 6  onto the surface to be coated at a flow rate of at least 0.20 sccm per square centimeter of wafer surface;   flowing hydrogen in said CVD chamber in conjunction with said flow of WF 6  ; and   flowing SiH 4  in said chamber in conjunction with said flowing of WF 6  and hydrogen, and at a rate of at least one-fifth of said WF 6  flow;     depositing a high-step-coverage portion of said integrated film to a thickness of at least 50% of the total integrated film thickness at a total pressure of from 20 Torr to 100 Torr comprising steps of: flowing WF 6  onto the surface to be coated at a flow rate of at least 0.15 sccm per square centimeter of wafer surface;   flowing hydrogen onto the surface to be coated in conjunction with flowing WF 6  ; and     depositing a low-stress portion of said integrated film at a total pressure of from 20 to 100 Torr comprising steps of: flowing WF 6  onto the surface to be coated at a flow rate of no more than about 0.05 sccm per square centimeter of wafer surface; and   flowing hydrogen onto the surface to be coated in conjunction with flowing WF 6  ;     the coating gases injected onto the wafer surface through a gas distribution device at a distance of no more than about 3.8 cm.